Topic 1 Specification Notes

Explain the importance of water as solvent in transport, including its dipole nature.

Water is a solvent therefore some substances dissolve in it
Water transports substances. Substances are transported more easily if they’re dissolved in solvent
Transports substances such as glucose and oxygen around animals and plants
One molecule of water is 1 atom of oxygen joined to 2 atoms of hydrogen by shared electrons
Because shared negative hydrogen electrons are pulled towards the 02, the other side of each hydrogen atom is left with a slight positive charge
Unshared negative electrons on the 02 atom give it a slight negative charge
This makes water a dipolar molecule where it has a slight positive charge on one side and a slight negative charge on the other
Negatively charged 02 atom of water attract the positively charged hydrogen atoms of another water molecule. This attraction is known as hydrogen bonding.

Waters dipole nature makes it very cohesive (attraction between 2 molecules of the same type)
This enables the water to flow making it suitable for transporting substances
Waters dipole nature makes it a very good solvent
Because the water is dipolar, the positive end is attracted to negative ions and the negative end is attracted to positive ions. Therefore, ions become completely surrounded by water molecules which causes them to dissolve:

Distinguish between monosaccharides, disaccharides and polysaccharides and relate their structures to their rules in providing and storing energy.

Monosaccharide: a single carbohydrate (e.g. glucose). They are joined by glycosidic bonds.

Disaccharide: 2 monosaccharides joined together though a condensation reaction. Examples of disaccharides are maltose, sucrose and lactose:

Monosaccharides joined by glycosidic bonds
Disaccharide
Glucose + glucose maltose Glucose + galactose lactose Glucose + fructose
Sucrose

Polysaccharide: more than 2 monosaccharides join together to form one long chain. Most important polysaccharides are glucose (main energy storage material in humans) and starch (main energy storage material in plants).

Starch:
Main energy storage molecule in plants
Mixture of Amylose and Amylopectin (2 polysaccharides)
Amylose is an unbranched, long chain of glucose held together by 1-4 glycosidic bonds. It has a coiled structure and is very compact, therefore a brilliant storage molecule.
Amylopectin is a long, brained chain of glucose held together by 1-4 and 1-6 glycosidic bonds. Side branches give enzymes access to the molecules for quick breakdown therefore releasing starch/glucose efficiently

Glycogen
Main energy storage material in animals
Very similar to amylopectin
Has 1-4 and 1-6 glycosidic bonds
Lots of side branches therefore stored glucose is released quickly
Very compact therefore good for storage

Describe how monosaccharides join to make disaccharides (sucrose, lactose and maltose) and polysaccharides (glycogen and amylose) through condensation reactions forming glycosidic bonds and how these can be split through hydrolysis

Monosaccharides join through condensation reactions in which the ‘H’ from one and the ‘OH’ from another bond to form H2O.

Monosaccharides split via hydrolysis in which H20 is added back into the equation:

Describe the synthesis of a triglyceride by the formation of ester bonds during a condensation reaction between a glycerol molecule and three fatty acids. Recognise differences between saturated and unsaturated fats.

Triglycerides are formed by condensation reactions; hydrogen atom on glycerol bonds with a hydroxyl group on the fatty acid therefore releasing a molecule of water.
They are broken by hydrolysis reaction; H2O is added to each ester bond to break it apart therefore splitting the triglyceride up into 3 fatty acids and 1 glyceride
Lipids can be saturated: found in animal fats; no double bonds between carbon atoms in their hydrocarbon tails; every carbon is attached to at least